Exploring the Document Object Model - HTML, CSS, and Dynamic HTML - page 899

Because every object aside from the window object is nested within other objects, you
can indicate an object's location within the hierarchy using the notation

object1 . object2 . object3 ...
where object1 is at the top of the hierarchy, object2 is a child of object1 , object3 is
a child of object2 , and so on. Thus, to reference the document object displayed within
the browser window, you could use:

window.document
You do not always have to use a complete reference detailing the entire object hierarchy.
For example, when you simply use the document object reference, JavaScript assumes
that you are referring to the document displayed within the current browser window. If
your script works with multiple browser windows, you might need to explicitly indicate
the window containing the document object you want to access. For now, all of the
scripts you'll write will apply to the currently active document.

Referencing Object Collections
When more than one of the same type of object exists, these objects are organized into
structures called object collections . For example, the object reference

document.images
references all of the inline image objects in the current document—and implicitly within
the current browser window. Figure 13-6 lists some other examples of object collections
found within the document , navigator , and window objects.

Figure 13-6 Object collections

Object Collection References

document.anchors

All anchors marked with the <a> tag

document.applets

All applets

document.embeds

All embed elements

document.forms

All Web forms

document. fname .elements

All form elements within the form fname

document.images

All inline images

document.links

All hypertext links

document.plugins

All plug-ins in the document

document.styleSheets

All style sheet elements

navigator.plugins

All plug-ins supported by the browser

navigator.mimeTypes

All MIME types supported by the browser

window.frames

All frames within the current browser window

To reference a specific object within a collection, you can use either

collection [ idref ]

or

collection . idref

where collection is a reference to the object collection, and idref is either an index
number representing the position of the object in the collection array or the value of the
id attribute assigned to the element. As with JavaScript's Array object, the first object in